UNIT B: Human Body Systems

Chapter 8: Human Organization Chapter 9: Digestive System: Section 9.1 Chapter 10: Circulatory System and Lymphatic System Chapter 11: Respiratory System Chapter 12: Nervous System Chapter 13: Urinary System Chapter 14: Reproductive System UNIT B: Human Body Systems

UNIT B Chapter 9: Digestive System In this chapter, you will learn about the structure and function of the digestive system. Chapter 9: Digestive System • What is our current understanding of the structure and function of the digestive system, including the stomach? • Which substances produced by the stomach and other organs help with the chemical breakdown of foods? Alexis St. Martin was an unexpected live test subject for Dr. William Beaumont’s research on how the digestive system works. TO PREVIOUS SLIDE

UNIT B Chapter 9: Digestive System Section 9.1 The digestive system is involved in the ingestion and digestion of food and elimination of indigestible material. Digestion takes place within the digestive tract, which begins with the mouth and ends with the anus. Digestion involves mechanical and chemical digestion. Mechanical digestion: chewing of food, and churning and mixing of food in the stomach Chemical digestion: enzymes break macromolecules down into small organic molecules 9.1 The Digestive Tract TO PREVIOUS SLIDE

UNIT B Chapter 9: Digestive System Section 9.1 Figure 9.1 The human digestive tract. The upper part of the tract includes the mouth, pharynx, esophagus, stomach, and small intestine. The large intestine consists of the cecum, the colon (ascending, transverse, descending, and sigmoid colons), the rectum, and the anus. Note also the location of the accessory organs of digestion: the pancreas, the liver, and the gall bladder. TO PREVIOUS SLIDE

UNIT B Chapter 9: Digestive System Section 9.1 The mouth takes food into the body. Teeth: involved in chewing food Tongue: composed of skeletal muscle and involved in forming the bolus (a mass of food that is ready for swallowing) Roof of the mouth: composed of a hard palate and a soft palate; prevents ingested food from entering the nasal cavity Tonsils: contain lymphoid tissue that protect against infections Salivary glands: produce saliva to keep the mouth moist; saliva contains an enzyme that digests starch The Mouth TO PREVIOUS SLIDE

UNIT B Chapter 9: Digestive System Section 9.1 The pharynx is a passageway that receives air from the nasal cavities and food from the mouth. Swallowing (a reflex action) occurs in the pharynx. The soft palate moves back to close off the nasopharynx The trachea moves up under the epiglottis to cover the glottis (the opening to the larynx (voice box)) During swallowing, food enters the epiglottis because the air passages are blocked The Pharynx TO PREVIOUS SLIDE

UNIT B Chapter 9: Digestive System Section 9.1 Figure 9.2 Swallowing. When food is swallowed, the soft palate closes off the nasopharynx and the epiglottis covers the glottis, forcing the bolus to pass down the esophagus. Therefore, a person does not breathe while swallowing. TO PREVIOUS SLIDE

UNIT B Chapter 9: Digestive System Section 9.1 TO PREVIOUS SLIDE

UNIT B Chapter 9: Digestive System Section 9.1 The esophagus is a long muscular tube that moves food from the mouth to the stomach by peristalsis. Peristalsis (rhythmic muscular contractions) pushes food along the esophagus and through the digestive tract to the stomach. The Esophagus TO PREVIOUS SLIDE

UNIT B Chapter 9: Digestive System Section 9.1 The stomach is an organ that receives food from the esophagus, mechanically and chemically digests food, and moves food into the small intestine. The Stomach TO PREVIOUS SLIDE

UNIT B Chapter 9: Digestive System Section 9.1 Structure and Function of the Stomach The human stomach has thick walls with folds (called rugae) that allow it to expand and fill with food. Lining of the stomach: has gastric glands that secrete gastric juice containing mucus and digestive enzymes Wall of the stomach: Three muscle layers (longitudinal, circular, oblique) Responsible for moving and churning food (mechanical digestion), and mixing food with gastric juice to break it down (chemical digestion) TO PREVIOUS SLIDE

UNIT B Chapter 9: Digestive System Section 9.1 Alcohol and other liquids are absorbed in the stomach, but most solid food is not. When food leaves the stomach, it is a thick, soupy liquid called chyme. Chyme enters the small intestine by way of the pyloric sphincter. TO PREVIOUS SLIDE

UNIT B Chapter 9: Digestive System Section 9.1 Figure 9.3 Anatomy of the stomach. a. The stomach has a thick wall with folds that allow it to expand and fill with food. b. The mucosa contains gastric glands, which secrete gastric juice containing mucus and digestive enzymes. TO PREVIOUS SLIDE

UNIT B Chapter 9: Digestive System Section 9.1 The small intestine receives chyme from the stomach and completes the digestion of food. Macromolecules are broken down into nutrients, which are absorbed in the small intestine and pass into the blood. The Small Intestine TO PREVIOUS SLIDE

UNIT B Chapter 9: Digestive System Section 9.1 Structure and Function of the Small Intestine The small intestine is composed of three parts. Duodenum: upper part of the small intestine Contains a bile duct that delivers bile from the liver and pancreatic juice from the pancreas Enzymes in pancreatic juice complete food digestion Jejunum: middle part of small intestine Ileum: lower part of small intestine Contains lymphoid tissues involved in immune response to intestinal pathogens TO PREVIOUS SLIDE

UNIT B Chapter 9: Digestive System Section 9.1 Structure and Function of the Small Intestine The wall of the small intestine contains villi, which increase the surface area to improve the absorption of nutrients. Villi: fingerlike projections that contain microvilli Microvilli increase the surface area of the villus for the absorption of nutrients Each villus contains blood capillaries and a small lymphatic capillary called a lacteal Nutrients are absorbed into the blood capillaries and the lacteals, which carry them to body cells TO PREVIOUS SLIDE

UNIT B Chapter 9: Digestive System Section 9.1 Figure 9.4 Anatomy of the small intestine. The wall of the small intestine has folds that bear fingerlike projections called villi. Microvilli, which project from the villi, absorb the products of digestion into the blood capillaries and the lacteals of the villi. TO PREVIOUS SLIDE

UNIT B Chapter 9: Digestive System Section 9.1 Regulation of Digestive Secretions Digestive secretions are controlled by the nervous system and hormones. After eating a meal: The stomach produces the hormone gastrin Gastrin: stimulates the gastric glands to secrete more gastric juice The duodenal wall produces the hormones secretin and CCK Secretin and CCK: stimulate the pancreas to secrete pancreatic juice and the gall bladder to secrete bile TO PREVIOUS SLIDE

UNIT B Chapter 9: Digestive System Section 9.1 Figure 9.5 Hormonal control of digestive gland secretions. Gastrin (blue), produced by the lower part of the stomach, enters the bloodstream and thereafter stimulates the stomach to produce more digestive juices. Secretin (green) and CCK (purple), produced by the duodenal wall, stimulate the pancreas to secrete its digestive juices and the gall bladder to release bile. TO PREVIOUS SLIDE

UNIT B Chapter 9: Digestive System Section 9.1 The large intestine absorbs water, salts, and some vitamins. It also stores indigestible material until it is eliminated as feces. The Large Intestine TO PREVIOUS SLIDE

UNIT B Chapter 9: Digestive System Section 9.1 Structure and Function of the Large Intestine • The large intestine includes the cecum, colon, rectum, and anal canal. • Cecum: a small pouch that forms the first part of the large intestine • Contains the appendix or vermiform appendix, which may play a role in fighting infection Figure 9.6 Junction of the small intestine and the large intestine. The cecum is the blind end of the large intestine. The appendix is attached to the cecum. TO PREVIOUS SLIDE

UNIT B Chapter 9: Digestive System Section 9.1 Structure and Function of the Large Intestine Colon: includes the ascending, transverse, descending, and sigmoid colon Rectum: the last part of the large intestine; opens at the anus Anus: rectum opening; site of defecation (expulsion of feces) TO PREVIOUS SLIDE

UNIT B Chapter 9: Digestive System Section 9.1 Defecation Reflex When feces are forced into the rectum by peristalsis, a defecation reflex occurs Figure 9.7 Defecation reflex. The accumulation of feces in the rectum causes it to stretch, which initiates a reflex action resulting in rectal contraction and expulsion of the fecal material. TO PREVIOUS SLIDE

UNIT B Chapter 9: Digestive System Section 9.1 Defecation Reflex Eliminating feces from the body is a way the digestive system maintains homeostasis Feces are about three-quarters water and one-quarter solids Solids: bacteria, fibre, and other indigestible materials Bacteria break down some indigestible material, and produce some vitamins that our bodies can absorb Water that is unsafe for drinking has a high number of coliform (intestinal) bacteria, indicating that a significant amount of feces has entered the water TO PREVIOUS SLIDE

UNIT B Chapter 9: Digestive System Section 9.1 List the parts of the human digestive tract that food passes through, and note whether chemical and/or mechanical digestion occurs in each. Compare the major functions of the small intestine and the large intestine. Discuss strategies that might help obese people lose weight by inhibiting the secretion and/or activity of certain hormones. Check Your Progress TO PREVIOUS SLIDE

UNIT B Chapter 9: Digestive System Section 9.1 TO PREVIOUS SLIDE

UNIT B: Human Body Systems